Which organism is an occasional cause of respiratory tract infections and is rapidly urease positive?

• A. Escherichia coli
• B. Bordetella bronchiseptica
• C. Campylobacter fetus
• D. Brucella abortus

Answer: (B)

This item hinges on recognizing a respiratory pathogen that shows rapid urease activity in the lab. Bordetella bronchiseptica is an occasional cause of respiratory tract infections in humans, especially in those with underlying lung conditions or weakened immunity. A key lab clue is its rapid urease positivity, meaning it quickly hydrolyzes urea to ammonia, producing a quick positive result in the urease test. This trait helps differentiate it from other bacteria listed: E. coli is not typically a respiratory pathogen and has a different urease pattern; Campylobacter fetus mainly causes gastrointestinal or systemic infections rather than respiratory disease; Brucella abortus is primarily associated with systemic brucellosis. Therefore, the combination of an occasional human respiratory infection and rapid urease positivity points to Bordetella bronchiseptica.